Nocardia-derived metabolites as promising antibacterial and larvicidal agents against Anopheles stephensi (Diptera: Culicidae)

Nocardia species produce diverse bioactive secondary metabolites, with potential applications against antibiotic resistance and vector-borne diseases. This study characterizes a metabolite from Nocardia fluminea strain N2, isolated from soils in Tehran, Iran, and evaluates its dual antibacterial and larvicidal activities. The strain, identified via 16S rRNA sequencing, and its metabolite production was monitored. Antibacterial efficacy was assessed using agar well diffusion and Minimum Inhibitory Concentration (MIC) assays, while larvicidal toxicity was evaluated by determining the Lethal Concentration 50 (LC₅₀) and 90 (LC₉₀). The metabolite's chemical composition was elucidated using High-Performance Liquid Chromatography (HPLC) and mass spectrometry. The metabolite exhibited potent antibacterial effects, demonstrating significant inhibition zones (>15 mm) and low MIC against Escherichia coli (6.67 μg/mL) and Salmonella typhimurium (2.67 μg/mL). In larvicidal assays against Anopheles stephensi, the metabolite showed time-dependent efficacy, with LC₅₀ values decreasing from 399 mg/L at 24 h to 353 mg/L at 72 h. Structural analysis suggested a novel compound with a molecular weight of 738 Da. Our findings identify the N. fluminea N2 metabolite as a promising dual-function agent for combating bacterial pathogens and malaria vectors.